Story highlights

The verdict can be changed only if a court rules the judge misapplied law, Phelps says

Sentence must be found to be "shockingly inappropriate" if appeal is to succeed, she says

South African prosecutors will appeal the verdict and the sentence in the Oscar Pistorius case, a spokesman for the country's National Prosecuting Authority told CNN on Monday.

A judge sentenced Pistorius to five years in prison last week after finding the double-amputee track star guilty of culpable homicide, or negligent killing, in the shooting death of his girlfriend, Reeva Steenkamp.

Pistorius acknowledged shooting Steenkamp in February 2013. Prosecutors claim he wanted to kill her; Pistorius said he mistook her for an intruder and her killing was a tragic accident.

The appeal doesn't necessarily mean either the verdict or the sentence against Pistorius will be thrown out, said CNN legal analyst Kelly Phelps. And it's even less likely he will be freed at the end of what's likely to be a six-month process, she said.

"There's no real prospect of his acquittal out of this," she said.

Prosecutors are arguing that Judge Thokozile Masipa misinterpreted a complex South African standard defining a technical form of intent that proved to be a central aspect of the case, Phelps said.

As a result, prosecutors argue, he should not have been convicted on the culpable homicide charge chosen by the judge.

Prosecutors originally took Pistorius to trial on a murder charge.

In explaining her sentence, Masipa concluded that Pistorius did not intend to kill Steenkamp.

But critics of the verdict have argued the judge didn't correctly apply the intent standard, which is broader in South African law than what it typically means in casual conversation, Phelps said.

In their appeal of the sentence, prosecutors would have to prove the five years given by Masipa is "shockingly inappropriate" in light of sentencing guidelines and similar cases, according to Phelps.

Prosecutor Gerrie Nel called for a minimum sentence of 10 years, saying the negligence in Pistorius' actions "borders on intent."

If an appeals court finds that five years is "shockingly inappropriate," the court could set the sentence aside and issue a new one, she said.

But appeals courts in South Africa are reluctant to get involved in sentencing decisions, Phelps said.

Pistorius' uncle, Arnold Pistorius, told CNN's Robyn Curnow, "We take note of the announcement made by the state. The legal process must take its course."